Abstract
BackgroundThe effects of low muscle glycogen on molecular markers of protein synthesis and myogenesis before and during aerobic exercise with carbohydrate ingestion is unclear. The purpose of this study was to determine the effects of initiating aerobic exercise with low muscle glycogen on mTORC1 signaling and markers of myogenesis.MethodsEleven men completed two cycle ergometry glycogen depletion trials separated by 7-d, followed by randomized isocaloric refeeding for 24-h to elicit low (LOW; 1.5 g/kg carbohydrate, 3.0 g/kg fat) or adequate (AD; 6.0 g/kg carbohydrate, 1.0 g/kg fat) glycogen. Participants then performed 80-min of cycle ergometry (64 ± 3% VO2peak) while ingesting 146 g carbohydrate. mTORC1 signaling (Western blotting) and gene transcription (RT-qPCR) were determined from vastus lateralis biopsies before glycogen depletion (baseline, BASE), and before (PRE) and after (POST) exercise.ResultsRegardless of treatment, p-mTORC1Ser2448, p-p70S6KSer424/421, and p-rpS6Ser235/236 were higher (P < 0.05) POST compared to PRE and BASE. PAX7 and MYOGENIN were lower (P < 0.05) in LOW compared to AD, regardless of time, while MYOD was lower (P < 0.05) in LOW compared to AD at PRE, but not different at POST.ConclusionInitiating aerobic exercise with low muscle glycogen does not affect mTORC1 signaling, yet reductions in gene expression of myogenic regulatory factors suggest that muscle recovery from exercise may be reduced.
Highlights
Reducing muscle glycogen through sustained aerobic exercise followed by low carbohydrate, high fat feeding increases fat oxidation and decreases carbohydrate oxidation during subsequent exercise bouts [1,2,3,4]
The most novel finding from the current study was that performing aerobic exercise with low muscle glycogen content resulted in lower PAX7 and MYOGENIN expression before and after exercise compared to adequate glycogen
Reductions in the transcription of these myogenic-related genes may impede muscle recovery from exercise [27]. It appears that differences in PAX7, MYOD, and MYOGENIN between LOW and AD were primarily driven by lower expression at PRE
Summary
Reducing muscle glycogen through sustained aerobic exercise followed by low carbohydrate, high fat feeding increases fat oxidation and decreases carbohydrate oxidation during subsequent exercise bouts [1,2,3,4]. Concurrent with transcriptional changes in fatty acid metabolism are reductions in pyruvate dehydrogenase (PDH) activity which spares glycogen by reducing carbohydrate oxidation during exercise [10, 11]. These acute molecular adaptations to initiating aerobic exercise with low muscle glycogen persist even when carbohydrate is ingested during the exercise bout [12]. The effects of low muscle glycogen on molecular markers of protein synthesis and myogenesis before and during aerobic exercise with carbohydrate ingestion is unclear. The purpose of this study was to determine the effects of initiating aerobic exercise with low muscle glycogen on mTORC1 signaling and markers of myogenesis
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